The present invention relates to the froth flotation of finely-divided coal particles for separation of ash therefrom and more particularly to a new frothing agent or frother which enhances the coal recovery in the froth flotation process.
Coalification is a natural process which results in the deposits of combustible carbonaceous solids in combination with some non-combustible mineral matter. Most coal cleaning is carried out by gravity separation methods utilizing jigs, shaking tables, heavy media or cyclones, and like techniques. The fine coal therefrom has been incorporated into clean coal or simply discarded in the past; however, due to economic and environmental considerations gained by recovery of the fine coal fraction, fine coal beneficiation has become a necessity in most coal operations requiring any degree of preparation. Froth flotation is one method which has been practiced for cleaning the fine coal.
The use of froth flotation to effect a separation of pyritic sulfur and ash particles from coal can be achieved only if liberation of these unwanted particles from the coal has taken place. Most high-grade coals are flotable naturally due to their hydrophobic surface and typically only require a frothing agent for effecting flotation. A frothing agent imparts elasticity to the air bubble, enhances particle-bubble attachment so that the coal is buoyed to the surface of the slurry. The floatability of coal can vary within a given seam at a mine depending upon the exposure of the locale to weathering elements or the blending of coals from different seams. Bituminous and lower grade coals either possess an oxidized condition as mined or undergo oxidation (weathering) when the coal is stored or stockpiled for later processing. Coal that has been oxidized does not respond well to froth flotation. As the degree of oxidation increases, coal becomes increasingly hydrophilic and, therefore, less coal readily can be floated. Heretofore, oxidized coal which was not flotable was discarded in the tailing of the flotation process with little attempt to recover this loss being undertaken.
Conventional frothing agents or frothers in the coal flotation process generally have been short-chain alkanols, terpene alcohols such as alpha-terpineol, short-chain glycols, sorbitol derivatives, ethoxylated alcohols, and mixed alkylene oxide glycol ethers. While such alcohol frothers function in the coal float, the need for improved alcohol frothers yet exists. The present invention provides improved high coal recoveries with improvements in coal quality utilizing a novel alcohol promoter which is highly effective and can be inexpensive to manufacture.